Multiplexing and transmission of multiple data streams in a wireless multi-carrier communication system

ABSTRACT

Techniques for multiplexing and transmitting multiple data streams are described. Transmission of the multiple data streams occurs in “super-frames”. Each super-frame has a predetermined time duration and is further divided into multiple (e.g., four) frames. Each data block for each data stream is outer encoded to generate a corresponding code block. Each code block is partitioned into multiple subblocks, and each data packet in each code block is inner encoded and modulated to generate modulation symbols for the packet. The multiple subblocks for each code block are transmitted in the multiple frames of the same super-frame, one subblock per frame. Each data stream is allocated a number of transmission units in each super-frame and is assigned specific transmission units to achieve efficient packing. A wireless device can select and receive individual data streams.

This application is a continuation of U.S. patent application Ser. No.10/932,586 entitled “Multiplexing and Transmission of Multiple DataStreams in a Wireless Multi-Carrier Communication System,” filed Sep. 1,2004, issued as U.S. Pat. No. 7,221,680, which claims the benefit ofprovisional U.S. Application Ser. No. 60/499,741 entitled “A Method forMultiplexing and Transmitting Multiple Multimedia Streams to MobileTerminals over Terrestrial Radio Links,” filed Sep. 2, 2003, andprovisional U.S. Application Ser. No. 60/559,740 entitled “Multiplexingand Transmission of Multiple Data Streams in a Wireless Multi-CarrierCommunication System,” filed Apr. 5, 2004.

BACKGROUND

I. Field

The present invention relates generally to communication, and morespecifically to techniques for multiplexing and transmitting multipledata streams in a wireless multi-carrier communication system.

II. Background

A multi-carrier communication system utilizes multiple carriers for datatransmission. These multiple carriers may be provided by orthogonalfrequency division multiplexing (OFDM), some other multi-carriermodulation techniques, or some other construct. OFDM effectivelypartitions the overall system bandwidth into multiple orthogonalsubbands. These subbands are also referred to as tones, carriers,subcarriers, bins, and frequency channels. With OFDM, each subband isassociated with a respective subcarrier that may be modulated with data.

A base station in a multi-carrier system may simultaneously transmitmultiple data streams for broadcast, multicast, and/or unicast services.A data stream is a stream of data that may be of independent receptioninterest to a wireless device. A broadcast transmission is sent to allwireless devices within a designated coverage area, a multicasttransmission is sent to a group of wireless devices, and a unicasttransmission is sent to a specific wireless device. For example, a basestation may broadcast a number of data streams for multimedia (e.g.,television) programs via a terrestrial radio link for reception bywireless devices. This system may employ a conventional multiplexing andtransmission scheme such as, for example, Digital VideoBroadcasting-Terrestrial (DVB-T) or Integrated Services DigitalBroadcasting-Terrestrial (ISDB-T). Such a scheme would first multiplexall of the data streams to be transmitted onto a single high-ratecomposite stream and then process (e.g., encode, modulate, andup-convert) the composite stream to generate a modulated signal forbroadcast via the radio link.

A wireless device within the coverage area of the base station may beinterested in receiving only one or few specific data streams among themultiple data streams carried by the composite stream. The wirelessdevice would need to process (e.g., down-convert, demodulate, anddecode) a received signal to obtain a high-rate decoded data stream andthen demultiplex this stream to obtain the one or few specific datastreams of interest. This type of processing may not be a problem forreceiver units intended to be powered on all the time, such as thoseused in homes. However, many wireless devices are portable and poweredby internal batteries. Continuous demodulation and decoding of thehigh-rate composite stream to recover just one or few data streams ofinterest consumes significant amounts of power. This can greatly shortenthe “ON” time for the wireless devices, which is undesirable.

There is therefore a need in the art for techniques to transmit multipledata streams in a multi-carrier system such that they can be received bywireless devices, with minimal power consumption.

SUMMARY

Techniques for multiplexing and transmitting multiple data streams in amanner to facilitate power-efficient and robust reception of individualdata streams by wireless devices are described herein. Each data streamis processed separately based on a coding and modulation scheme (e.g.,an outer code, an inner code, and a modulation scheme) selected for thatstream to generate a corresponding data symbol stream. This allows thedata streams to be individually recovered by the wireless devices. Eachdata stream is also allocated certain amount of resources fortransmission of that stream. The allocated resources are given in“transmission units” on a time-frequency plane, where each transmissionunit corresponds to one subband in one symbol period and may be used totransmit one data symbol. The data symbols for each data stream aremapped directly onto the transmission units allocated to the stream.This allows the wireless devices to recover each data streamindependently, without having to process the other data streams beingtransmitted simultaneously.

In an embodiment, transmission of the multiple data streams occurs in“super-frames”, with each super-frame having predetermined time duration(e.g., on the order of a second or few seconds). Each super-frame isfurther divided into multiple (e.g., two, four, or some other number of)frames. For each data stream, each data block is processed (e.g., outerencoded) to generate a corresponding code block. Each code block ispartitioned into multiple subblocks, and each subblock is furtherprocessed (e.g., inner encoded and modulated) to generate acorresponding subblock of modulation symbols. Each code block istransmitted in one super-frame, and the multiple subblocks for the codeblock are transmitted in the multiple frames of the super-frame, onesubblock per frame. The partitioning of each code block into multiplesubblocks, the transmission of these subblocks over multiple frames, andthe use of block coding across the subblocks of the code block providerobust reception performance in slowly time-varying fading channels.

Each data stream may be “allocated” a variable number of transmissionunits in each super-frame depending on the stream's payload in thesuper-frame, the availability of transmission units in the super-frame,and possibly other factors. Each data stream is also “assigned” specifictransmission units within each super-frame using an assignment schemethat attempts to (1) pack the transmission units for all data streams asefficiently as possible, (2) reduce the transmission time for each datastream, (3) provide adequate time-diversity, and (4) minimize the amountof signaling to indicate the specific transmission units assigned toeach data stream. Overhead signaling for various parameters of the datastreams (e.g., the coding and modulation scheme used for each datastream, the specific transmission units assigned to each data stream,and so on) may be transmitted prior to each super-frame and may also beembedded within the data payload of each data stream. This allows awireless device to determine the time-frequency location of each desireddata stream in the upcoming super-frame. The wireless device may poweron only when the desired data stream is transmitted, using the embeddedoverhead signaling, and thereby minimize power consumption.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and nature of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 shows a wireless multi-carrier system;

FIG. 2 shows an exemplary super-frame structure;

FIGS. 3A and 3B illustrate transmission of one data block and multipledata blocks, respectively, on a physical layer channel (PLC) in asuper-frame;

FIG. 4 shows a frame structure in a time-frequency plane;

FIG. 5A shows a burst-TDM (time division multiplex) scheme;

FIG. 5B shows a cycled-TDM scheme;

FIG. 5C shows a burst-TDM/FDM (frequency division multiplex) scheme;

FIG. 6 shows an interlaced subband structure;

FIG. 7A shows assignment of slots to PLCs in rectangular patterns;

FIG. 7B shows assignment of slots to PLCs in “zigzag” segments;

FIG. 7C shows assignment of slots to two joint PLCs in rectangularpatterns;

FIG. 8 illustrates coding of a data block with an outer code;

FIGS. 9A and 9B show assignment of slots for one data block using onesubband group and a maximum allowable number of subband groups,respectively;

FIG. 9C shows assignment of slots for six data blocks;

FIGS. 9D and 9E show assignment of slots to two joint PLCs withrectangular patterns stacked horizontally and vertically, respectively;

FIG. 10 shows a process for broadcasting multiple data streams;

FIG. 11 shows a block diagram of a base station;

FIG. 12 shows a block diagram of a wireless device;

FIG. 13 shows a block diagram of a transmit (TX) data processor, achannelizer, and an OFDM modulator at the base station; and

FIG. 14 shows a block diagram of a data stream processor for one datastream.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

The multiplexing and transmission techniques described herein may beused for various wireless multi-carrier communication systems. Thesetechniques may also be used for broadcast, multicast, and unicastservices. For clarity, these techniques are described for an exemplarymulti-carrier broadcast system.

FIG. 1 shows a wireless multi-carrier broadcast system 100. System 100includes a number of base stations 110 that are distributed throughoutthe system. A base station is generally a fixed station and may also bereferred to as an access point, a transmitter, or some otherterminology. Neighboring base stations may broadcast the same ordifferent content. Wireless devices 120 are located throughout thecoverage area of the system. A wireless device may be fixed or mobileand may also be referred to as a user terminal, a mobile station, userequipment, or some other terminology. A wireless device may also be aportable unit such as a cellular phone, a handheld device, a wirelessmodule, a personal digital assistant (PDA), and so on.

Each base station 110 may broadcast multiple data streams simultaneouslyto wireless devices within its coverage area. These data streams may befor multimedia content such as video, audio, tele-text, data,video/audio clips, and so on. For example, a single multimedia (e.g.,television) program may be sent in three separate data streams forvideo, audio, and data. A single multimedia program may also havemultiple audio data streams, e.g., for different languages. Forsimplicity, each data stream is sent on a separate physical layerchannel (PLC). There is thus a one-to-one relationship between datastreams and PLCs. A PLC may also be called a data channel, a trafficchannel, or some other terminology.

FIG. 2 shows an exemplary super-frame structure that may be used forbroadcast system 100. Data transmission occurs in units of super-frames210. Each super-frame has a predetermined time duration, which may beselected based on various factors such as, for example, the desiredstatistical multiplexing for the data streams, the desired amount oftime diversity, acquisition time for the data streams, bufferrequirements for the wireless devices, and so on. A larger super-framesize provides more time diversity and better statistical multiplexing ofthe data streams being transmitted, so that less buffering may berequired for individual data streams at the base station. However, alarger super-frame size also results in a longer acquisition time for anew data stream (e.g., at power-on or when switching between datastreams), requires larger buffers at the wireless devices, and also haslonger decoding latency or delay. A super-frame size of approximatelyone second may provide good tradeoff between the various factorsdescribed above. However, other super-frame sizes (e.g., a quarter, ahalf, two, or four seconds) may also be used. Each super-frame isfurther divided into multiple equal-sized frames 220. For the embodimentshown in FIG. 2, each super-frame is divided into four frames.

The data stream for each PLC is encoded and modulated based on a codingand modulation scheme selected for that PLC. In general, a coding andmodulation scheme comprises all of the different types of encoding andmodulation to be performed on a data stream. For example, a coding andmodulation scheme may comprise a particular coding scheme and aparticular modulation scheme. The coding scheme may comprise errordetection coding (e.g., a cyclic redundancy check (CRC)), forward errorcorrection coding, and so on, or a combination thereof. The codingscheme may also indicate a particular code rate of a base code. In anembodiment that is described below, the data stream for each PLC isencoded with a concatenated code comprised of an outer coder and aninner code and is further modulated based on a modulation scheme. Asused herein, a “mode” refers to a combination of an inner code rate anda modulation scheme.

FIG. 3A illustrates the transmission of a data block on a PLC in asuper-frame. The data stream to be sent on the PLC is processed in datablocks. Each data block contains a particular number of information bitsand is first encoded using an outer code to obtain a corresponding codeblock. Each code block is partitioned into four subblocks, and the bitsin each subblock are further encoded using an inner code and then mappedto modulation symbols, based on the mode selected for the PLC. The foursubblocks of modulation symbols are then transmitted in the four framesof one super-frame, one subblock per frame. The transmission of eachcode block over four frames provides time diversity and robust receptionperformance in a slowly time-varying fading channel.

FIG. 3B illustrates the transmission of multiple (N_(bl)) data blocks ona PLC in a super-frame. Each of the N_(bl) data blocks is encodedseparately using the outer code to obtain a corresponding code block.Each code block is further partitioned into four subblocks, which areinner encoded and modulated based on the mode selected for the PLC andthen transmitted in the four frames of one super-frame. For each frame,N_(bl) subblocks for the N_(bl) code blocks are transmitted in a portionof the frame that has been allocated to the PLC.

Each data block may be encoded and modulated in various manners. Anexemplary concatenated coding scheme is described below. To simplify theallocation and assignment of resources to the PLCs, each code block maybe divided into four equal-sized subblocks that are then transmitted inthe same portion or location of the four frames in one super-frame. Inthis case, the allocation of a super-frame to the PLCs is equivalent tothe allocation of a frame to the PLCs. Hence, resources can be allocatedto the PLCs once every super-frame.

Each PLC may be transmitted in a continuous or non-continuous manner,depending on the nature of the data stream being carried by that PLC.Thus, a PLC may or may not be transmitted in any given super-frame. Foreach super-frame, an “active” PLC is a PLC that is being transmitted inthat super-frame. Each active PLC may carry one or multiple data blocksin the super-frame.

Referring back to FIG. 2, each super-frame 210 is preceded by a pilotand overhead section 230. In an embodiment, section 230 includes (1) oneor more pilot OFDM symbols used by the wireless devices for framesynchronization, frequency acquisition, timing acquisition, channelestimation, and so on, and (2) one or more overhead OFDM symbols used tocarry overhead signaling information for the associated (e.g.,immediately following) super-frame. The overhead information indicates,for example, the specific PLCs being transmitted in the associatedsuper-frame, the specific portion of the super-frame used to send thedata block(s) for each PLC, the outer code rate and mode used for eachPLC, and so on. The overhead OFDM symbol(s) carries overhead signalingfor all PLCs sent in the super-frame. The transmission of the pilot andoverhead information in a time division multiplexed (TDM) manner allowsthe wireless devices to process this section with minimal ON time. Inaddition, overhead information pertaining to each PLC's transmission inthe next super-frame may be embedded in one of the PLC's transmitteddata blocks in the current super-frame. The embedded overheadinformation allows the wireless device to recover the PLC's transmissionin the next super-frame without having to check the overhead OFDMsymbol(s) sent in that super-frame. Thus, the wireless devices mayinitially use the overhead OFDM symbols to determine the time-frequencylocation of each desired data stream, and may subsequently power on onlyduring the time that the desired data stream is transmitted using theembedded overhead signaling. These signaling techniques may providesignificant savings in power consumption and allow the wireless devicesto receive content using standard batteries. Since the outer code rateand mode used for each PLC typically do not vary on a super-frame basis,the outer code rate and mode may be sent on a separate control channeland do need not be sent in every super-frame.

FIG. 2 shows a specific super-frame structure. In general, a super-framemay be defined to be of any time duration and may be divided into anynumber of frames. Pilot and overhead information may also be sent inother manners different from the manner shown in FIG. 2. For example,overhead information may be sent on dedicated subbands using frequencydivision multiplexing (FDM).

FIG. 4 shows the structure of one frame on a time-frequency plane. Thehorizontal axis represents time, and the vertical axis representsfrequency. Each frame has a predetermined time duration, which is givenin units of OFDM symbol periods (or simply, symbol periods). Each OFDMsymbol period is the time duration to transmit one OFDM symbol(described below). The specific number of symbol periods per frame(N_(spf)) is determined by the frame duration and the symbol periodduration, which in turn is determined by various parameters such as theoverall system bandwidth, the total number of subbands (N_(tsb)), andthe cyclic prefix length (described below). In an embodiment, each framehas a duration of 297 symbol periods (or N_(spf)=297). Each frame alsocovers the N_(tsb) total subbands, which are given indices of 1 throughN_(tsb).

With OFDM, one modulation symbol may be sent on each subband in eachsymbol period, i.e., each transmission unit. Of the N_(tsb) totalsubbands, N_(dsb) subbands may be used for data transmission and arereferred to as “data” subbands, N_(psb) subbands may be used for pilotand are referred to as “pilot” subbands, and the remaining N_(gsb)subbands may be used as “guard” subbands (i.e., no data or pilottransmission), where N_(tsb)=N_(dsb)+N_(psb)+N_(gsb). The number of“usable” subbands is equal to the number of data and pilot subbands, orN_(usb)=N_(dsb)+N_(psb). In an embodiment, broadcast system 100 utilizesan OFDM structure having 4096 total subbands (N_(tsb)=4096), 3500 datasubbands (N_(dsb)=3500), 500 pilot subbands (N_(psb)=500), and 96 guardsubbands (N_(gsb)=96). Other OFDM structures with different number ofdata, pilot, usable, and total subbands may also be used. In each OFDMsymbol period, N_(dsb) data symbols may be sent on the N_(dsb) datasubbands, N_(psb) pilot symbols may be sent on the N_(psb) pilotsubbands, and N_(gsb) guard symbols are sent on the N_(gsb) guardsubbands. As used herein, a “data symbol” is a modulation symbol fordata, a “pilot symbol” is a modulation symbol for pilot, and a “guardsymbol” is a signal value of zero. The pilot symbols are known a prioriby the wireless devices. The N_(dsb) data symbols in each OFDM symbolmay be for one or multiple PLCs.

In general, any number of PLCs may be transmitted in each super-frame.For a given super-frame, each active PLC may carry one or multiple datablocks. In one embodiment, a specific mode and a specific outer coderate is used for each active PLC, and all data blocks for the PLC areencoded and modulated in accordance with this outer code rate and modeto generate corresponding code blocks and subblocks of modulationsymbols, respectively. In another embodiment, each data block may beencoded and modulated in accordance with a specific outer code rate andmode to generate a corresponding code block and subblocks of modulationsymbols, respectively. In any case, each code block contains a specificnumber of data symbols, which is determined by the mode used for thatcode block.

Each active PLC in a given super-frame is allocated a specific amount ofresources to transmit that PLC in the super-frame. The amount ofresources allocated to each active PLC is dependent on (1) the number ofcode blocks to be sent on the PLC in the super-frame, (2) the number ofdata symbols in each code block, and (3) the number of code blocks,along with the number of data symbols per code block, to be sent onother PLCs. Resources may be allocated in various manners. Two exemplaryallocation schemes are described below.

FIG. 5A shows a burst-TDM allocation scheme. For this scheme, eachactive PLC is allocated all N_(dsb) data subbands in one or more OFDMsymbol periods. For the example shown in FIG. 5A, PLC I is allocated alldata subbands in symbol periods 1 through 3, PLC 2 is allocated all datasubbands in symbol periods 4 and 5, and PLC 3 is allocated all datasubbands in symbol periods 6 through 9. For this scheme, each OFDMsymbol contains data symbols for only one PLC. The bursts of OFDMsymbols for different PLCs are time division multiplexed within a frame.

If consecutive OFDM symbols are assigned to each active PLC, then theburst-TDM can minimize the transmission time for the PLCs. However, theshort transmission time for each PLC also results in less timediversity. Since an entire OFDM symbol is allocated to one PLC, thegranularity of the resource allocation (i.e., the smallest unit that maybe allocated to a PLC) for each frame is one OFDM symbol. The number ofinformation bits that may be sent in one OFDM symbol is dependent on themode used to process the information bits. For the burst-TDM scheme, thegranularity of the allocation is then dependent on mode. The granularityis larger for higher order modes that are capable of carrying moreinformation bits per data symbol. In general, a larger granularityadversely impacts “packing” efficiency, which refers to the percentageof the frame that is actually used to carry data. If an active PLC doesnot require the data-carrying capacity of an entire OFDM symbol, thenthe excess capacity is wasted and reduces packing efficiency.

FIG. 5B shows a cycled-TDM allocation scheme. For this scheme, theactive PLCs in the super-frame are arranged into L groups, where L>1. Aframe is also divided into L sections, and each PLC group is assigned toa respective section of the frame. For each group, the PLCs in the groupare cycled through, and each PLC is allocated all N_(dsb) data subbandsin one or more OFDM symbol periods in the assigned section. For theexample shown in FIG. 5B, PLC 1 is allocated all data subbands in symbolperiod 1, PLC 2 is allocated all data subbands in symbol period 2, PLC 3is allocated all data subbands in symbol period 3, PLC 1 is allocatedall data subbands in symbol period 4, and so on. Compared to burst-TDM,the cycled-TDM scheme may provide more time diversity, reduce receiverbuffering requirements and peak decoding rate, but increase the receiveron-time to receive a given PLC.

FIG. 5C shows a burst-TDM/FDM allocation scheme. For this scheme, eachactive PLC is allocated one or more data subbands in one or more symbolperiods. For the example shown in FIG. 5C, PLC 1 is allocated datasubbands 1 through 3 in symbol periods 1 through 8, PLC 2 is allocateddata subbands 4 and 5 in symbol periods 1 through 8, and PLC 3 isallocated data subbands 6 through 9 in symbol periods 1 through 8. Forthe burst-TDM/FDM scheme, each OFDM symbol may contain data symbols formultiple PLCs. The bursts of data symbols for different PLCs are timeand frequency division multiplexed within a frame.

Since the payload of each PLC may be distributed over time as well asfrequency, the burst-TDM/FDM scheme may increase the transmission timefor the PLC. However, this also provides more time diversity. Thetransmission time for each PLC may be reduced by allocating moresubbands to the PLC. For the burst-TDM/FDM scheme, the granularity ofthe resource allocation may be selected based on a tradeoff betweenpacking efficiency and overhead signaling. In general, smallergranularity results in better packing efficiency but also requires moreoverhead signaling to indicate the resources allocated to each PLC. Theinverse is generally true with larger granularity. The description belowassumes the use of the burst-TDM/FDM scheme.

In an embodiment, the N_(usb) usable subbands are divided into N_(gr)groups of usable subbands. One of the N_(gr) groups may then contain thepilot subbands. For the remaining groups, the number of data subbands inone group determines the granularity of the resource allocation. TheN_(usb) usable subbands may be arranged into the N_(gr) groups invarious manners. In one subband grouping scheme, each group containsN_(spg) consecutive usable subbands, where N_(usb)=N_(gr)·N_(spg). Inanother subband grouping scheme, each group contains N_(spg) usablesubbands that are pseudo-randomly distributed across the N_(usb) usablesubbands. In yet another subband grouping scheme, each group containsN_(spg) usable subbands that are uniformly spaced across the N_(usb)usable subbands.

FIG. 6 shows an interlaced subband structure 600 that may be used forthe burst-TDM/FDM scheme. The N_(usb) usable subbands are arranged intoN_(gr) disjoint groups, which are labeled as subband groups 1 throughN_(gr). The N_(gr) subband groups are disjoint in that each of theN_(usb) usable subbands belongs to only one group. Each subband groupcontains N_(spg) usable subbands that are uniformly distributed acrossthe N_(usb) total usable subbands such that consecutive subbands in thegroup are spaced apart by N_(sp) subbands. In an embodiment, the 4000usable subbands (N_(usb)=4000) are arranged into eight groups(N_(gr)=8), each group contains 500 usable subbands (N_(spg)=500), andthe usable subbands for each group are spaced apart by eight subbands(N_(sp)=8). The usable subbands in each group are thus interlaced withthe usable subbands in the other N_(gr)-1 groups. Each subband group isalso referred to as an “interlace”.

The interlaced subband structure provides various advantages. First,better frequency diversity is achieved since each group includes usablesubbands from across the entire system bandwidth. Second, a wirelessdevice may recover data symbols sent on each subband group by performinga “partial” (e.g., 512-point) fast Fourier transform (FFT) instead of afull (e.g., 4096-point) FFT, which may reduce the power consumed by thewireless device. Techniques for performing a partial FFT are describedin commonly assigned U.S. patent application Ser. No. 10/775,719,entitled “Subband-Based Demodulator for an OFDM-based CommunicationSystem,” filed Feb. 9, 2004. The following description assumes the useof the interlaced subband structure shown in FIG. 6.

Each PLC may be allocated resources on a super-frame by super-framebasis. The amount of resources to allocate to each PLC in eachsuper-frame is dependent on the payload of the PLC for that super-frame.A PLC may carry a fixed-rate data stream or a variable-rate data stream.In an embodiment, the same mode is used for each PLC even if the datarate of the data stream carried by that PLC changes. This ensures thatthe coverage area for the data stream remains approximately constantregardless of data rate, so that reception performance is not dependenton data rate. The variable rate nature of a data stream is handled byvarying the amount of resources allocated to the PLC in eachsuper-frame.

Each active PLC is allocated resources from the time-frequency plane, asshown in FIG. 4. The allocated resources for each active PLC may begiven in units of “transmission slots” (or simply, “slots”). A slotcorresponds to one group of (e.g., 500) data subbands or, equivalently,one group of modulation symbols in one symbol period. N_(gr) slots areavailable in each symbol period and may be assigned slot indices 1through N_(gr). Each slot index may be mapped to one subband group ineach symbol period based on a slot-to-interlace mapping scheme. One ormore slot indices may be used for an FDM pilot, and the remaining slotindices may be used for the PLCs. The slot-to-interlace mapping may besuch that the subband groups (or interlaces) used for the FDM pilot havevarying distances to the subband groups used for each slot index. Thisallows all slot indices used for the PLCs to achieve similarperformance.

Each active PLC is allocated at least one slot in a super-frame. Eachactive PLC is also assigned specific slot(s) in the super-frame. The“allocation” process provides each active PLC with the amount orquantity of resources, whereas the “assignment” process provides eachactive PLC with the specific resources within the super-frame. Forclarity, allocation and assignment may be viewed as separate processes.In practice, allocation and assignment are typically performed jointlysince allocation may be affected by assignment, and vice versa. In anycase, the assignment may be performed in a manner to achieve thefollowing goals:

-   -   1. Minimize the transmission time for each PLC to reduce ON time        and power consumption by the wireless devices to recover the        PLC;    -   2. Maximize time diversity for each PLC to provide robust        reception performance;    -   3. Constrain each PLC to be within a specified maximum bit rate;        and    -   4. Minimize buffering requirements for the wireless devices.        The maximum bit rate indicates the maximum number of information        bits that may be transmitted in each OFDM symbol for one PLC.        The maximum bit rate is typically set by the decoding and        buffering capabilities of the wireless devices. Constraining        each PLC to be within the maximum bit rate ensures that the PLC        can be recovered by wireless devices having the prescribed        decoding and buffering capabilities.

Some of the goals listed above conflict with one another. For example,goals 1 and 2 conflict, and goals 1 and 4 conflict. A resourceallocation/assignment scheme attempts to achieve a balance betweenconflicting goals and may allow for flexibility in the setting ofpriority.

Each active PLC in a super-frame is allocated a certain number of slotsbased on the payload of the PLC. Different PLCs may be allocateddifferent numbers of slots. The specific slots to assign to each activePLC may be determined in various manners. Some exemplary slot assignmentschemes are described below.

FIG. 7A shows assignment of slots to PLCs in rectangular patterns, inaccordance with a first slot assignment scheme. Each active PLC isassigned slots arranged in a two-dimensional (2-D) rectangular pattern.The size of the rectangular pattern is determined by the number of slotsallocated to the PLC. The vertical dimension (or height) of therectangular pattern is determined by various factors such as the maximumbit rate. The horizontal dimension (or width) of the rectangular patternis determined by the number of allocated slots and the verticaldimension.

To minimize transmission time, an active PLC may be assigned as manysubband groups as possible while conforming to the maximum bit rate. Themaximum number of information bits that may be sent in one OFDM symbolmay be encoded and modulated with different modes to obtain differentnumbers of data symbols, which then require different numbers of datasubbands for transmission. The maximum number of data subbands that maybe used for each PLC may thus be dependent on the mode used for the PLC.

In an embodiment, the rectangular pattern for each active PLC includescontiguous subband groups (in indices) and contiguous symbol periods.This type of assignment reduces the amount of overhead signaling neededto specify the rectangular pattern and further makes the slotassignments for the PLCs more compact, which then simplifies the packingof the PLCs within a frame. The frequency dimension of the rectangularpattern may be specified by the starting subband group and the totalnumber of subband groups for the rectangular pattern. The time dimensionof the rectangular pattern may be specified by the starting symbolperiod and the total number of symbol periods for the rectangularpattern. The rectangular pattern for each PLC may thus be specified withfour parameters.

For the example shown in FIG. 7A, PLC 1 is assigned 8 slots in a 2×4rectangular pattern 712, PLC 2 is assigned 12 slots in a 4×3 rectangularpattern 714, and PLC 3 is assigned 6 slots in a 1×6 rectangular pattern716. The remaining slots in the frame may be assigned to other activePLCs. As shown in FIG. 7A, different rectangular patterns may be usedfor different active PLCs. To improve packing efficiency, the activePLCs may be assigned slots in a frame, one PLC at a time and in asequential order determined by the number of slots allocated to eachPLC. For example, slots in the frame may be assigned first to the PLCwith the largest number of allocated slots, then to the PLC with thenext largest number of allocated slots, and so on, and then finally tothe PLC with the smallest number of allocated slots. The slots may alsobe assigned based on other factors such as, for example, the priority ofthe PLCs, the relationship among the PLCs, and so on.

FIG. 7B shows assignment of slots to PLCs in “sinusoidal” or “zigzag”segments, in accordance with a second slot assignment scheme. For thisscheme, a frame is divided into N_(st) “strips”. Each strip covers atleast one subband group and further spans a contiguous number of symbolperiods, up to the maximum number of symbol periods in a frame. TheN_(st) strips may include the same or different numbers of subbandgroups. Each of the active PLCs is mapped to one of the N_(st) stripsbased on various factors. For example, to minimize transmission time,each active PLC may be mapped to the strip with the most number ofsubband groups allowed for that PLC.

The active PLCs for each strip are assigned slots in the strip. Theslots may be assigned to the PLCs in a specific order, e.g., using avertical zigzag pattern. This zigzag pattern selects slots from low tohigh subband group indices, for one symbol period at a time, and fromsymbol periods 1 to N_(spf). For the example shown in FIG. 7B, strip 1includes subband groups 1 through 3. PLC 1 is assigned a segment 732containing 10 slots from subband group 1 in symbol period 1 throughsubband group 1 in symbol period 4. PLC 2 is assigned a segment 734containing 4 slots from subband group 2 in symbol period 4 throughsubband group 2 in symbol period 5. PLC 3 is assigned a segment 736containing 6 slots from subband group 3 in symbol period 5 throughsubband group 2 in symbol period 7. The remaining slots in strip 1 maybe assigned to other active PLCs mapped to this strip.

The second slot assignment scheme effectively maps all of the slots in atwo-dimensional (2-D) strip onto a one-dimensional (1-D) strip and thenperforms 2-D slot assignment using one dimension. Each active PLC isassigned a segment within the strip. The assigned segment may bespecified by two parameters: the start of the segment (which may begiven by the starting subband and symbol period) and the length of thesegment. An additional parameter is used to indicate the specific stripto which the PLC is mapped. In general, the segment assigned to eachactive PLC may include any number of slots. However, less overheadsignaling is required to identify the assigned segments if the segmentsizes are constrained to be in multiple (e.g., 2 or 4) slots.

The second slot assignment scheme can assign slots to active PLCs in asimple manner. Also, tight packing may be achieved for each strip sincethe slots within the strip may be consecutively assigned to the PLCs.The vertical dimensions of the N_(st) strips may be defined to match theprofile of all active PLCs in the super-frame so that (1) as many PLCsas possible are sent using the largest number of data subbands allowedfor the PLCs and (2) the N_(st) strips are packed as fully as possible.

FIGS. 7A and 7B show two exemplary slot assignment schemes. Theseschemes facilitate efficient packing of PLCs in each frame. Theseschemes also reduce the amount of overhead signaling needed to indicatethe specific slots assigned to each active PLC. Other slot assignmentschemes may also be used, and this is within the scope of the invention.For example, a slot assignment scheme may partition a frame into strips,the active PLCs for the frame may be mapped to the available strips, andthe PLCs for each strip may be assigned rectangular patterns within thestrip. The strips may have different heights (i.e., different numbers ofsubband groups). The rectangular patterns assigned to the PLCs for eachstrip may have the same height as that of the strip but may havedifferent widths (i.e., different number of symbol periods) determinedby the number of slots allocated to the PLCs.

For simplicity, FIGS. 7A and 7B show the assignment of slots toindividual PLCs. For some services, multiple PLCs may be jointly decodedby wireless devices and are referred to as “joint” PLCs. This may be thecase, for example, if multiple PLCs are used for the video and audiocomponents of a single multimedia program and are jointly decoded torecover the program. The joint PLCs may be allocated the same ordifferent number of slots in each super-frame, depending on theirpayloads. To minimize the ON time, the joint PLCs may be assigned slotsin consecutive symbol periods so that the wireless devices do not needto “wake up” multiple times within a frame to receive these PLCs.

FIG. 7C shows assignment of slots to two joint PLCs 1 and 2 based on thefirst slot assignment scheme. In a first embodiment, the joint PLCs areassigned slots in rectangular patterns that are stacked horizontally orside-by-side. For the example shown in FIG. 7C, PLC 1 is allocated 8slots in a 2×4 rectangular pattern 752, and PLC 2 is allocated 6 slotsin a 2×3 rectangular pattern 754, which is located directly to the rightof pattern 752. This embodiment allows each PLC to be decoded as soon aspossible, which may reduce buffering requirements at the wirelessdevices.

In a second embodiment, the joint PLCs are assigned slots in rectangularpatterns that are stacked vertically. For the example shown in FIG. 7C,PLC 3 is allocated 8 slots in a 2×4 rectangular pattern 762, and PLC 4is allocated 6 slots in a 2×3 rectangular pattern 764, which is locateddirectly above pattern 762. The total number of subband groups used forthe joint PLCs may be such that these joint PLCs collectively conform tothe maximum bit rate. For the second embodiment, the wireless devicesmay store the received data symbols for the joint PLCs in separatebuffers until they are ready for decoding. The second embodiment mayreduce the ON time for the joint PLCs relative to the first embodiment.

In general, any number of PLCs may be jointly decoded. The rectangularpatterns for the joint PLCs may span the same or different numbers ofsubband groups, which may be constrained by the maximum bit rate. Therectangular patterns may also span the same or different numbers ofsymbol periods. The rectangular patterns for some sets of joint PLCs maybe stacked horizontally while the rectangular patterns for other sets ofjoint PLCs may be stacked vertically.

Joint PLCs may also be assigned zigzag segments. In one embodiment, themultiple PLCs to be jointly decoded are assigned consecutive segments inthe same strip. In another embodiment, the multiple PLCs are assignedsegments in different strips, and the segments overlap in time as muchas possible in order to reduce the ON time to recover these PLCs.

In general, each data stream may be encoded in various manners. In anembodiment, each data stream is encoded with a concatenated codecomprised of an outer code and an inner code. The outer code may be ablock code such as a Reed-Solomon (RS) code or some other code. Theinner code may be a Turbo code (e.g., a parallel concatenatedconvolutional code (PCCC) or a serially concatenated convolutional code(SCCC)), a convolutional code, a low-density parity-check (LDPC) code,or some other code.

FIG. 8 shows an exemplary outer coding scheme using a Reed-Solomon code.A data stream for a PLC is partitioned into data packets. In anembodiment, each data packet contains a predetermined number (L) ofinformation bits. As a specific example, each data packet may contain976 information bits. Other packet sizes and formats may also be used.The data packets for the data stream are written into rows of a memory,one packet per row. After K data packets have been written into K rows,block coding is performed column-wise, one column at a time. In anembodiment, each column contains K bytes (one byte per row) and isencoded with an (N, K) Reed-Solomon code to generate a correspondingcodeword that contains N bytes. The first K bytes of the codeword aredata bytes (which are also called systematic bytes) and the last N−Kbytes are parity bytes (which may be used by a wireless device for errorcorrection). The Reed-Solomon coding generates N−K parity bytes for eachcodeword, which are written to rows K+1 through N in the memory afterthe K rows of data. An RS block contains K rows of data and N−K rows ofparity. In an embodiment, N=16 and K is a configurable parameter, e.g.,K ε{12, 14, 16}. The Reed-Solomon code is disabled when K=N. A CRCvalue, e.g., 16-bits in length, is then appended to each data packet (orrow) of the RS block followed by the addition of (e.g., 8) zero (tail)bits to reset the inner encoder to a known state. The resulting longer(e.g., 1000 bits) packet is subsequently encoded by the inner code togenerate a corresponding inner coded packet. A code block contains Nouter coded packets for the N rows of the RS block, where each outercoded packet may be a data packet or a parity packet. The code block isdivided into four subblocks, and each subblock contains four outer codedpackets if N=16.

In an embodiment, each data stream may be transmitted with or withoutlayered coding, where the term “coding” in this context refers tochannel encoding rather than source encoding at a transmitter. A datastream may be comprised of two substreams, which are called a basestream and an enhancement stream. In one embodiment, the base stream maycarry information sent to all wireless devices within the coverage areaof the base station. The enhancement stream may carry additionalinformation sent to wireless devices observing better channelconditions. With layered coding, the base stream is encoded andmodulated in accordance with a first mode to generate a first modulationsymbol stream, and the enhancement stream is encoded and modulated inaccordance with a second mode to generate a second modulation symbolstream. The first and second modes may be the same or different. The twomodulation symbol streams are then combined to obtain one data symbolstream.

Table 1 shows an exemplary set of eight modes that may be supported bythe system. Let m denote the mode, where m=1, 2, . . . , 8. Each mode isassociated with a specific modulation scheme (e.g., QPSK or 16-QAM) anda specific inner code rate R_(in)(m) (e.g., 1/3, 1/2, or 2/3). The firstfive modes are for “regular” coding with only the base stream, and thelast three modes are for layered coding with the base and enhancementstreams. For simplicity, the same modulation scheme and inner code rateare used for both the base and enhancement streams for each layeredcoding mode.

TABLE 1 Inner Number Slots/ Number Slots/ Modulation Code Rate PacketSubblock Mode m Scheme R_(in)(m) N_(spp)(m) N_(sps)(m) 1 QPSK ⅓ 3 12 2QPSK ½ 2 8 3 16-QAM ⅓ 1.5 6 4 16-QAM ½ 1 4 5 16-QAM ⅔ 0.75 3 6 QPSK/QPSK⅓ 3 12 7 QPSK/QPSK ½ 2 8 8 QPSK/QPSK ⅔ 1.5 6

Table 1 also shows various transmission parameters for each mode. Thefourth column of Table 1 indicates the number of slots needed totransmit one packet for each mode, which assumes a packet size ofapproximately 1000 information bits and 500 data subbands per slot. Thefifth column indicates the number of slots needed to transmit onesubblock of four packets for each mode. Different numbers of subbandgroups may be used for a PLC for all of the modes. The use of moresubband groups results in shorter transmission time but also providesless time diversity.

As an example for mode 1, one data block with K data packets may beencoded to generate 16 coded packets. Each data packet contains 1000information bits. Since mode 1 uses code rate R_(in)(1)=1/3, each codedpacket contains 3000 code bits and may be transmitted on 1500 datasubbands (or three subband groups) using QPSK, which can carry two codebits per data symbol. The four coded packets for each subblock may besent in 12 slots. Each subblock may be transmitted in a rectangularpattern of, e.g., dimension 4×3, 3×4, 2×6, or 1×12, where the firstvalue P in dimension P×Q is for the number of subband groups and thesecond value Q is for the number of symbol periods for the rectangularpattern.

Table 1 shows an exemplary design, which is provided to show variousparameters that may impact subband allocation and assignment. Ingeneral, the system may support any number of modes, and each mode maycorrespond to a different coding and modulation scheme. For example,each mode may correspond to a different combination of modulation schemeand inner code rate. To simplify the design of the wireless devices, thesystem may utilize a single inner code (e.g., with a base code rate of1/3 or 1/5), and different code rates may be achieved by puncturing ordeleting some of the code bits generated by the inner code. However, thesystem may also utilize multiple inner codes. The maximum allowablenumber of subband groups for each mode may be different and possiblybased on the maximum bit rate.

In general, one or multiple data blocks may be sent on an active PLC ineach super-frame. The number of data blocks to be sent per super-frameis dependent on the data rate of the data stream being sent on the PLC.The number of slots (N_(slot)) to allocate to the PLC per frame is equalto the number of data blocks (N_(bl)) being sent on the PLC in thesuper-frame times the number of slots required for one subblock, orN_(slot)=N_(bl)·N_(sps)(m), where N_(sps)(m) is dependent on the modeused for the PLC. If the PLC carries a large number of data blocks inone super-frame (for a high-rate data stream), then it is desirable touse as many subband groups as possible in order to minimize thetransmission time for the PLC. For example, if the PLC carries 16 datablocks in one super-frame, then the transmission time per frame usingmode 1 is 192=16·12 symbol periods using one subband group (which is 65%of the frame duration) and only 48=192/4 symbol periods using foursubband groups (which is 16.25% of the frame duration). The transmissiontime for the PLC may thus be substantially shortened by using moresubband groups.

FIG. 9A shows assignment of slots in a super-frame for one code block(N_(bl)=1) using one subband group, which is equivalent to assignment ofslots in a frame for one subblock. For the embodiment described above,each subblock contains four packets that are labeled 1, 2, 3, and 4 inFIG. 9A. Each packet is transmitted in a different number of slots foreach of modes 1 through 5 in Table 1. The four packets 1 through 4 forone subblock may be transmitted on one subband group in 12 symbolperiods for mode 1, 8 symbol periods for mode 2, 6 symbol periods formode 3, 4 symbol periods for mode 4, and 3 symbol periods for mode 5.For modes 3 and 5, two packets may share the same slot. Each packet maybe decoded as soon as the entire packet is received.

FIG. 9B shows assignment of slots in a super-frame for one code block(N_(bl)=1) using 4, 4, 3, 2, and 1 subband group for modes m=1, 2, 3, 4,and 5, respectively. The four packets in one subblock may be sent in a4×3 rectangular pattern 932 for mode 1, a 4×2 rectangular pattern 934for mode 2, a 3×2 rectangular pattern 936 for mode 3, a 2×2 rectangularpattern 938 for mode 4, and a 1×4 rectangular pattern 940 for mode 5.

In one embodiment, the four packets in one subblock are transmitted in avertical zigzag pattern 942 within a rectangular pattern, as shown inFIG. 9B. This embodiment reduces buffering requirements since eachpacket is transmitted in as few symbol periods as possible and there isonly one partial packet in any given symbol period. In anotherembodiment, the four packets are transmitted in a horizontal zigzagpattern 944. This embodiment provides more time diversity since eachpacket is transmitted over as many symbol periods as possible. However,the maximum bit rate may restrict the number of subband groups that maybe used, or additional buffering may be needed, since up to two packetsmay be received in full in the same symbol period using the horizontalzigzag pattern.

FIG. 9C shows assignment of slots in a super-frame for six code blocks(N_(bl)=6) using four subband groups. In this example, mode 2 is usedfor the PLC, each packet is sent in two slots, 24 packets are sent ineach frame for the six code blocks, and the PLC is allocated 48 slots ina 4×12 rectangular pattern 952 for each frame. The 24 packets may besent in various manners within rectangular pattern 952.

In a first embodiment, which is shown in FIG. 9C, the packets are sentin the rectangular pattern by cycling through the six code blocks. Foreach cycle through the six code blocks, one packet is selected from eachcode block, and the six packets for the six code blocks are sent usingthe vertical zigzag pattern. The six packets 1 for the code blocks aresent in a box 954 a, the six packets 2 for the code blocks are sent in abox 954 b, the six packets 3 for the code blocks are sent in a box 954c, and the six packets 4 for the code blocks are sent in a box 954 d.The j-th packet for the i-th code block is labeled as Bi Pj in FIG. 9C.

The first embodiment provides more time diversity across each code blocksince the four packets for the code block are sent over more symbolperiods. Packets sent in one symbol period are likely to suffer fromcorrelated erasures. For example, a deep fade during a symbol period maycause all packets sent in that symbol period to be decoded in error. Bysending packets from different code blocks in the same symbol period,the correlated (packet) erasures will be distributed over multiple codeblocks. This enhances the ability of the block decoder to correct theseerasures. The first embodiment also spaces the four packets for eachcode block as far apart in time as possible, which improves timediversity across the code block. For example, the four packets for codeblock 1 are sent in symbol periods 1, 4, 7, and 10, and are spaced apartby three symbol periods. The first embodiment also reduces bufferingrequirements since each packet is sent over as few symbol periods aspossible.

In a second embodiment, which is not shown in the figures, the packetsare selected by cycling through the N_(bl) code blocks, similar to thefirst embodiment, but the N_(bl) packets for each cycle are sent usingthe horizontal zigzag pattern within box 954. This embodiment mayprovide more time diversity across each packet. In a third embodiment,the four packets for one code block are sent first, the four packets foranother code block are sent next, and so on. This embodiment allows forearly recovery of some code blocks. Multiple code blocks may thus besent on a PLC in various manners.

As noted above, multiple PLCs may be intended to be jointly decoded.Each of the joint PLCs may carry any number of code blocks persuper-frame depending on the data rate of the data stream being sent onthe PLC. The total number of subband groups to use for the joint PLCsmay be limited by the maximum bit rate.

FIG. 9D shows assignment of slots in a super-frame to two joint PLCsusing horizontally stacked rectangular patterns. In this example, PLC 1carries two code blocks using mode 4 (e.g., for a video stream), andeight packets are sent in eight slots for each frame. PLC 2 carries onecode block using mode 2 (e.g., for an audio stream), and four packetsare sent in eight slots for each frame. The eight packets for PLC 1 aresent in a 2×4 rectangular pattern 962 by cycling through the two codeblocks and using the vertical zigzag pattern, as described above forFIG. 9C. The four packets for PLC 2 are sent in a 2×4 rectangularpattern 964 using the vertical zigzag pattern. Pattern 964 is stacked tothe right of pattern 962.

FIG. 9E shows assignment of slots in a super-frame to two joint PLCsusing vertically stacked rectangular patterns. The eight packets for PLC1 are sent in a 1×8 rectangular pattern 972 by cycling through the twocode blocks and using the vertical zigzag pattern, albeit with only onesubband group. The four packets for PLC 2 are sent in a 2×4 rectangularpattern 974 using the vertical zigzag pattern. Pattern 974 is stacked ontop of pattern 972. The use of the 1×8 rectangular pattern for PLC 1ensures that only two packets are sent in each symbol period, which maybe a restriction imposed by the maximum bit rate. A 2×4 rectangularpattern may be used for PLC 1, if allowed by the maximum bit rate, toreduce the total transmission time for both PLCs 1 and 2.

The examples shown in FIGS. 9D and 9E may be extended to cover anynumber of joint PLCs, any number of code blocks for each PLC, and anymode for each PLC. Slots may be assigned to the joint PLCs such that thetotal transmission time for these PLCs is minimized while conforming tothe maximum bit rate.

For the outer coding scheme shown in FIG. 8, the first K packets of eachcode block are for data, and the last N−K packets are for parity bits.Since each packet includes a CRC value, a wireless device can determinewhether each packet is decoded correctly or in error by re-computing theCRC value using the received information bits of the packet andcomparing the recomputed CRC value to the received CRC value. For eachcode block, if the first K packets are decoded correctly, then thewireless device does not need to process the last N−K packets. Forexample, if N=16, K=12, and the last four packets of a code block aresent in the fourth frame, then the wireless device does not need to wakeup in the last frame if the 12 data packets sent in the first threeframes are decoded correctly. Furthermore, any combination of up to N−Kincorrectly (inner) decoded packets may be corrected by the Reed-Solomondecoder.

For clarity, the description above is based on a concatenated codingscheme comprised of an outer code and an inner code and for theparameters given in Table 1. Other coding schemes may also be used forthe system. Furthermore, the same or different parameters may be usedfor the system. The subband allocation and assignment may be performedusing the techniques described herein and in accordance with thespecific coding scheme and parameters applicable to the system.

FIG. 10 shows a flow diagram of a process 1000 for broadcasting multipledata streams using the multiplexing and transmission techniquesdescribed herein. Process 1000 may be performed for each super-frame.

Initially, the active PLCs for the current super-frame are identified(block 1012). For each active PLC, at least one data block is processedin accordance with the outer code (and rate) selected for the PLC toobtain at least one code block, one code block for each data block(block 1014). Each active PLC is allocated a specific number oftransmission units based on the PLC's payload for the currentsuper-frame (block 1016). In general, the transmission units in thecurrent super-frame may be allocated to the active PLCs with any levelof granularity. For example, the transmission units may be allocated tothe active PLCs in slots, with each slot containing 500 transmissionunits. Specific transmission units in each frame of the currentsuper-frame are then assigned to each active PLC (block 1018). Block1016 determines the resource quantity allocated for each active PLC.Block 1018 provides the specific resource allocation for each active PLCand may be performed based on an assignment scheme. For example, thescheme that assigns rectangular patterns or the scheme that assignzigzag segments within strips may be used for block 1018. The allocationand assignment of transmission units may also be performed jointly sincethe allocation may be dependent on the packing efficiency achieved bythe assignment.

Each code block for each active PLC is partitioned into multiplesubblocks, one subblock for each frame (block 1020). Each packet in eachsubblock is then encoded by the inner code and mapped to modulationsymbols (block 1022). The inner code rate and modulation scheme used foreach PLC is determined by the mode selected for that PLC. The multiplesubblocks for each code block are then sent in the multiple frames ofthe current super-frame to achieve time diversity. For each frame of thecurrent super-frame, the data symbols in the subblock(s) to be sent inthat frame for each active PLC are mapped onto the transmission unitsassigned to the PLC (block 1024). A composite symbol stream is thenformed with (1) the multiplexed data symbols for all of the active PLCsand (2) pilot, overhead, and guard symbols (block 1026). The compositesymbol stream is further processed (e.g., OFDM modulated andconditioned) and broadcast to wireless devices in the system.

The multiplexing and transmission techniques described herein allow themultiple data streams sent in each super-frame to be independentlyrecoverable by a wireless device. A given data stream of interest may berecovered by (1) performing OFDM demodulation on all subbands or justthe subbands used for the data stream, (2) demultiplexing the detecteddata symbols for the data stream, and (3) decoding the detected datasymbols for the data stream. The other data streams need not becompletely or partially decoded in order to receive the desired datastream. Depending on the allocation and assignment scheme selected foruse, the wireless device may perform partial demodulation and/or partialdecoding of another data stream in order to recover the data stream ofinterest. For example, if multiple data streams share the same OFDMsymbol, then the demodulation of a selected data stream may result inpartial demodulation of an unselected data stream.

FIG. 11 shows a block diagram of a base station 110 x, which is one ofthe base stations in system 100. At base station 110 x, a transmit (TX)data processor 1110 receives multiple (N_(plc)) data streams (denoted as{d₁} through {d_(N) _(plc) }) from one or more data sources 1108, e.g.,multiple data sources for different services, where each service may becarried in one or more PLCs. TX data processor 1110 processes each datastream in accordance with the mode selected for that stream to generatea corresponding data symbol stream and provides N_(plc) data symbolstreams (denoted as {s₁} through {S_(N) _(plc) }) to a symbolmultiplexer (Mux)/channelizer 1120. TX data processor 1110 also receivesoverhead data (which is denoted as {d_(O)}) from a controller 1140,processes the overhead data in accordance with the mode used foroverhead data, and provides an overhead symbol stream (denoted as{s_(O)}) to channelizer 1120. An overhead symbol is a modulation symbolfor overhead data.

Channelizer 1120 multiplexes the data symbols in the N_(plc) data symbolstreams onto their assigned transmission units. Channelizer 1120 alsoprovides pilot symbols on the pilot subbands and guard symbols on theguard subbands. Channelizer 1120 further multiplexes pilot symbols andoverhead symbols in the pilot and overhead section preceding eachsuper-frame (see FIG. 2). Channelizer 1120 provides a composite symbolstream (denoted as {s_(C)}) that carries data, overhead, pilot, andguard symbols on the proper subbands and symbol periods. An OFDMmodulator 1130 performs OFDM modulation on the composite symbol streamand provides a stream of OFDM symbols to a transmitter unit (TMTR) 1132.Transmitter unit 1132 conditions (e.g., converts to analog, filters,amplifies, and frequency upconverts) the OFDM symbol stream andgenerates a modulated signal that then is transmitted from an antenna1134.

FIG. 12 shows a block diagram of a wireless device 120 x, which is oneof the wireless devices in system 100. At wireless device 120 x, anantenna 1212 receives the modulated signal transmitted by base station110 x and provides a received signal to a receiver unit (RCVR) 1214.Receiver unit 1214 conditions, digitizes, and processes the receivedsignal and provides a sample stream to an OFDM demodulator 1220. OFDMdemodulator 1220 performs OFDM demodulation on the sample stream andprovides (1) received pilot symbols to a channel estimator 1222 and (2)received data symbols and received overhead symbols to a detector 1230.Channel estimator 1222 derives a channel response estimate for the radiolink between base station 110 x and wireless device 120 x based on thereceived pilot symbols. Detector 1230 performs detection (e.g.,equalization or matched filtering) on the received data and overheadsymbols with the channel response estimate. Detector 1230 provides to asymbol demultiplexer (Demux)/dechannelizer 1240 “detected” data andoverhead symbols, which are estimates of the transmitted data andoverhead symbols, respectively. The detected data/overhead symbols maybe represented by log-likelihood ratios (LLRs) for the code bits used toform the data/overhead symbols, or by other representations. Channelestimator 1222 may also provide timing and frequency information to OFDMdemodulator 1220.

A controller 1260 obtains an indication of (e.g., user selection for)one or more specific data streams/PLCs to be recovered. Controller 1260then determines the resource allocation and assignment for each selectedPLC. If wireless device 120 x is acquiring the signal for the first time(e.g., initial acquisition), then the signaling information is obtainedfrom the overhead OFDM symbols decoded by a receive (RX) data processor1250. If wireless device 120 x is successfully receiving data blocks insuper-frames, then the signaling information may be obtained through theembedded overhead signaling that is part of at least one data block sentin each super-frame. This embedded overhead signaling indicates theallocation and assignment of the corresponding data stream/PLC in thenext super-frame. Controller 1260 provides a MUX_RX control todechannelizer 1240. Dechannelizer 1240 performs demultiplexing of thedetected data or overhead symbols for each symbol period based on theMUX_RX control and provides one or more detected data symbol streams ora detected overhead symbol stream, respectively, to RX data processor1250. In the case of the overhead OFDM symbols, RX data processor 1250processes the detected overhead symbol stream in accordance with themode used for overhead signaling and provides the decoded overheadsignaling to controller 1260. For the data symbol stream(s), RX dataprocessor 1250 processes each detected data symbol stream of interest,in accordance with the mode used for that stream, and provides acorresponding decoded data stream to a data sink 1252. In general, theprocessing at wireless device 120 x is complementary to the processingat base station 110 x.

Controllers 1140 and 1260 direct the operation at base station 110 x andwireless device 120 x, respectively. Memory units 1142 and 1262 providestorage for program codes and data used by controllers 1140 and 1260,respectively. Controller 1140 and/or a scheduler 1144 allocate resourcesto the active PLCs and further assign transmission units to each activePLC.

FIG. 13 shows a block diagram of an embodiment of TX data processor1110, channelizer 1120, and OFDM modulator 1130 at base station 110 x.TX data processor 1110 includes N_(plc) TX data stream processors 1310 aand 1310 p for the N_(plc) data streams and a data stream processor 1310q for the overhead data. Each TX data stream processor 1310independently encodes, interleaves, and modulates a respective datastream {d_(i)} to generate a corresponding data symbol stream {s_(i)}.

FIG. 14 shows a block diagram of a TX data stream processor 1310 i,which may be used for each of TX data stream processors 1310 in FIG. 13.TX data stream processor 1310 i processes one data stream for one PLC.Data stream processor 1310 i includes a base stream processor 1410 a, anenhancement stream processor 1410 b, and a bit-to-symbol mapping unit1430. Processor 1410 a processes a base stream for the PLC, andprocessor 1410 b processes an enhancement stream (if any) for the PLC.

Within base stream processor 1410 a, an outer encoder 1412 a encodeseach data block of base stream data in accordance with, e.g., aReed-Solomon code to generate an RS code block. An RS code blockconsists of N outer coded packets. Encoder 1412 a also appends a CRCvalue to each outer coded packet. This CRC value may be used by awireless device for error detection (i.e., to determine whether thepacket is decoded correctly or in error). An outer interleaver 1414 apartitions each code block into subblocks, interleaves (i.e., reorders)the packets among the different subblocks that are transmitted in eachframe, and buffers the subblocks transmitted in the different frames ofa super-frame. An inner encoder 1416 a then encodes each outer codedpacket of a subblock in accordance with, e.g., a Turbo code to generatean inner coded packet. An inner bit interleaver 1418 a interleaves thebits within each inner coded packet to generate a correspondinginterleaved packet. The encoding by the outer encoder 1412 a and innerencoder 1416 a increases the reliability of the transmission for thebase stream. The interleaving by outer interleaver 1414 a and innerinterleaver 1418 a provides time and frequency diversity, respectively,for the base stream transmission. A scrambler 1420 a randomizes the bitsin each encoded and bit interleaved packet with a PN sequence andprovides scrambled bits to mapping unit 1430.

Enhancement stream processor 1410 b similarly performs processing on theenhancement stream (if any) for the PLC. Processor 1410 b may use thesame inner code, outer code, and modulation scheme as those used forprocessor 1410 a, or different ones. Processor 1410 b provides scrambledbits for the enhancement stream to mapping unit 1430.

Mapping unit 1430 receives the scrambled bits for the base andenhancement streams, a gain G_(bs) for the base stream, and a gainG_(es) for the enhancement stream. The gains G_(bs) and G_(es) determinethe amount of transmit power to use for the base and enhancementstreams, respectively. Different coverage areas may be achieved for thebase and enhancement streams by transmitting these streams at differentpower levels. Mapping unit 1430 maps the received scrambled bits to datasymbols based on a selected mapping scheme and the gains G_(bs) andG_(es). The symbol mapping may be achieved by (1) grouping sets of Bscrambled bits to form B-bit binary values, where B≧1, and (2) mappingeach B-bit binary value to a data symbol, which is a complex value for apoint in a signal constellation for the selected modulation scheme. Iflayered coding is not used, then each data symbol corresponds to a pointin a signal constellation such as M-PSK or M-QAM, where M=2^(B). Iflayered coding is used, then each data symbol corresponds to a point ina complex signal constellation, which may or may not be formed by thesuperposition of two scaled signal constellations. For the embodimentdescribed above, the base and enhancement streams carry the same numberof code blocks for each super-frame. The code blocks for the base andenhancement streams may be transmitted simultaneously, as shown in FIG.14, or transmitted using TDM and/or FDM.

Referring back to FIG. 13, channelizer 1120 is implemented with amultiplexer 1320 that receives the N_(plc) data symbol streams, theoverhead symbol stream, pilot symbols, and guard symbols. Multiplexer1320 provides the data symbols, overhead symbols, pilot symbols, andguard symbols onto the proper subbands and symbol periods based on aMUX_TX control from controller 1140 and outputs the composite symbolstream, {s_(C)}. In assigning modulation symbols to the subband groups,a further level of (symbol) interleaving can be performed by assigningmodulation symbols in a pseudo-random fashion to the subbands withineach subband group. To simplify the assignment of subbands, the PLCs maybe assigned slots, as described above. The slots may then be mapped todifferent subband groups, e.g., in a pseudo-random fashion from onesymbol period to the next. This slot to subband group mapping ensuresthat the modulation symbols associated with a specific slot index havedifferent distances from the pilot subbands for different symbolperiods, which may improve performance.

OFDM modulator 1130 includes an inverse fast Fourier transform (IFFT)unit 1330 and a cyclic prefix generator 1332. For each symbol period,IFFT unit 1330 transforms each set of N_(tsb) symbols for the N_(tsb)total subbands to the time domain with an N_(tsb)-point IFFT to obtain a“transformed” symbol that contains N_(tsb) time-domain chips. To combatintersymbol interference (ISI), which is caused by frequency selectivefading, cyclic prefix generator 1332 repeats a portion of eachtransformed symbol to form a corresponding OFDM symbol. The repeatedportion is often called a cyclic prefix or guard interval. Cyclic prefixgenerator 1332 provides a stream of data chips (denoted as {c}) for thecomposite symbol stream, {s_(C)}.

The multiplexing and transmission techniques described herein may beimplemented by various means. For example, these techniques may beimplemented in hardware, software, or a combination thereof. For ahardware implementation, the processing units used to performmultiplexing and/or transmission at a base station may be implementedwithin one or more application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), processors, controllers, micro-controllers,microprocessors, other electronic units designed to perform thefunctions described herein, or a combination thereof The processingunits used to perform the complementary processing at a wireless devicemay also be implemented within one or more ASICs, DSPs, and so on.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 1142 or 1262 in FIG. 11) andexecuted by a processor (e.g., controller 1140 or 1260). The memory unitmay be implemented within the processor or external to the processor, inwhich case it can be communicatively coupled to the processor viavarious means as is known in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method of broadcasting and multicasting data ina wireless communication system, comprising: processing a plurality ofdata streams to obtain a plurality of data symbol streams, one datasymbol stream for each data stream; allocating transmission units toeach of the plurality of data streams, each transmission unitcorresponding to one symbol period and being usable to transmit one datasymbol in a subband; mapping data symbols in each data symbol stream torespective transmission units allocated to a corresponding data stream;and forming a composite symbol stream with overhead symbols and datasymbols, for the plurality of data streams, mapped to respectiveallocated transmission units of a current frame, wherein each of theplurality of data streams is independently recoverable by a receiverusing the overhead symbols included in the composite symbol stream, theoverhead symbols of the current frame indicating an allocation and anassignment of a corresponding data stream transmitted in another framethat is subsequent to the current frame.
 2. The method of claim 1,wherein T total subbands are usable for transmitting data symbols ineach symbol period used for broadcast and are allocable to multiple datastreams, where T>1.
 3. The method of claim 2 wherein multiple datastreams are allocated different groups of subbands in each symbol periodused for broadcast and multicast.
 4. The method of claim 3, wherein thesubbands in each group are distributed across the T total subbands, andwherein the subbands in each group are interlaced with the subbands inother groups in same symbol period.
 5. The method of claim 1, whereineach data stream is independently processed with a coding and modulationscheme selected for the data stream to obtain the corresponding datasymbol stream.
 6. The method of claim 1, wherein each of the pluralityof data streams is independently encoded using a base inner code and aninner code rate selected for the data stream.
 7. The method of claim 1,wherein transmission units are allocated to each data stream based on aninformation data rate of the data stream.
 8. The method of claim 1,wherein transmission units are allocated to the plurality of datastreams in each frame of a predetermined time duration.
 9. The method ofclaim 1, wherein the multi-carrier communication system utilizesorthogonal frequency division multiplexing (OFDM).
 10. The method ofclaim 1, further comprising: selecting at least one data stream forrecovery; determining the transmission units used for each selected datastream; obtaining by the receiver detected data symbols for eachselected data stream, each detected data symbol being an estimate of acorresponding data symbol broadcast by a transmitter; demodulatingdetected data symbols from transmission units used for each selecteddata stream onto a detected data symbol stream for the selected datastream, wherein at least one detected data symbol stream is obtained forthe at least one data stream selected for recovery; and processing eachof the at least one detected data symbol stream to obtain acorresponding decoded data stream.
 11. An apparatus in a wirelessbroadcast communication system, comprising: a data processor operativeto process a plurality of data streams to obtain a plurality of datasymbol streams, one data symbol stream for each data stream; acontroller operative to allocate transmission units to each of theplurality of data streams, each transmission unit corresponding to onesymbol period and being usable to transmit one data symbol in a subband;and a multiplexer operative to map data symbols in each data symbolstream to respective transmission units allocated to the correspondingdata stream and to form a composite symbol stream with overhead symbolsand data symbols, for the plurality of data streams, mapped torespective allocated transmission units of a current frame, wherein eachof the plurality of data streams is independently recoverable by areceiver using the overhead symbols included in the composite symbolstream, the overhead symbols of the current frame indicating anallocation and an assignment of a corresponding data stream transmittedin another frame that is subsequent to the current frame.
 12. Theapparatus of claim 11, wherein T total subbands are usable fortransmitting data symbols in each symbol period used for broadcast andare allocable to multiple data streams, where T>1.
 13. The apparatus ofclaim 12 wherein multiple data streams are allocated different groups ofsubbands in each symbol period used for broadcast and multicast.
 14. Theapparatus of claim 13, wherein the subbands in each group aredistributed across T total subbands, and wherein the subbands in eachgroup are interlaced with the subbands in other groups in same symbolperiod.
 15. The apparatus of claim 11, wherein each data stream isindependently processed with a coding and modulation scheme selected forthe data stream to obtain the corresponding data symbol stream.
 16. Theapparatus of claim 11, wherein each of the plurality of data streams isindependently encoded using a base inner code and an inner code rateselected for the data stream.
 17. The apparatus of claim 11, whereintransmission units are allocated to each data stream based on aninformation data rate of the data stream.
 18. The apparatus of claim 11,wherein transmission units are allocated to the plurality of datastreams in each frame of a predetermined time duration.
 19. Theapparatus of claim 11, wherein the multi-carrier communication systemutilizes orthogonal frequency division multiplexing (OFDM).
 20. Theapparatus of claim 11, wherein the receiver is configured to: select atleast one data stream for recovery; determine the transmission unitsused for each selected data stream; obtain detected data symbols foreach selected data stream, each detected data symbol being an estimateof a corresponding data symbol broadcast by a transmitter; demodulatedetected data symbols from transmission units used for each selecteddata stream onto a detected data symbol stream for the selected datastream, wherein at least one detected data symbol stream is obtained forthe at least one data stream selected for recovery; and process each ofthe at least one detected data symbol stream to obtain a correspondingdecoded data stream.
 21. An apparatus for broadcasting and multicastingdata in a wireless communication system, comprising: means forprocessing a plurality of data streams to obtain a plurality of datasymbol streams, one data symbol stream for each data stream; means forallocating transmission units to each of the plurality of data streams,each transmission unit corresponding to one symbol period and beingusable to transmit one data symbol in a subband; means for mapping datasymbols in each data symbol stream to respective transmission unitsallocated to the corresponding data stream; and means for forming acomposite symbol stream with overhead symbols and data symbols, for theplurality of data streams, mapped to respective allocated transmissionunits of a current frame, wherein each of the plurality of data streamsis independently recoverable by a receiver using the overhead symbolsincluded in the composite symbol stream, the overhead symbols of thecurrent frame indicating an allocation and an assignment of acorresponding data stream transmitted in another frame that issubsequent to the current frame.
 22. The apparatus of claim 21, whereinT total subbands are usable for transmitting data symbols in each symbolperiod used for broadcast and are allocable to multiple data streams,where T>1.
 23. The apparatus of claim 22, wherein multiple data streamsare allocated different groups of subbands in each symbol period usedfor broadcast and multicast.
 24. The apparatus of claim 23, wherein thesubbands in each group are distributed across T total subbands, andwherein the subbands in each group are interlaced with the subbands inother groups in same symbol period.
 25. The apparatus of claim 21,wherein each data stream is independently processed with a coding andmodulation scheme selected for the data stream to obtain thecorresponding data symbol stream.
 26. The apparatus of claim 21, whereineach of the plurality of data streams is independently encoded using abase inner code and an inner code rate selected for the data stream. 27.The apparatus of claim 21, wherein transmission units are allocated toeach data stream based on an information data rate of the data stream.28. The apparatus of claim 21, wherein transmission units are allocatedto the plurality of data streams in each frame of a predetermined timeduration.
 29. The apparatus of claim 21, wherein the multi-carriercommunication system utilizes orthogonal frequency division multiplexing(OFDM).
 30. The apparatus of claim 21, further comprising: means forselecting at least one data stream for recovery; means for determiningthe transmission units used for each selected data stream; means forobtaining by the receiver detected data symbols for each selected datastream, each detected data symbol being an estimate of a correspondingdata symbol broadcast by a transmitter; means for demodulating detecteddata symbols from transmission units used for each selected data streamonto a detected data symbol stream for the selected data stream, whereinat least one detected data symbol stream is obtained for the at leastone data stream selected for recovery; and means for processing each ofthe at least one detected data symbol stream to obtain a correspondingdecoded data stream.
 31. A non-transitory computer-readable storagemedium, in a wireless communication system, storing instructionsthereon, comprising: instructions to process a plurality of data streamsto obtain a plurality of data symbol streams, one data symbol stream foreach data stream; instructions to allocate transmission units to each ofthe plurality of data streams, each transmission unit corresponding toone symbol period and being usable to transmit one data symbol in asubband; instructions to map data symbols in each data symbol stream torespective transmission units allocated to the corresponding datastream; and instructions to form a composite symbol stream with overheadsymbols and data symbols, for the plurality of data streams, mapped torespective allocated transmission units of a current frame, wherein eachof the plurality of data streams is independently recoverable by areceiver using the overhead symbols included in the composite symbolstream, the overhead symbols of the current frame indicating anallocation and an assignment of a corresponding data stream transmittedin another frame that is subsequent to the current frame.
 32. Thecomputer-readable storage medium of claim 31, wherein T total subbandsare usable for transmitting data symbols in each symbol period used forbroadcast and are allocable to multiple data streams, where T>1.
 33. Thecomputer-readable storage medium of claim 32, wherein multiple datastreams are allocated different groups of subbands in each symbol periodused for broadcast and multicast.
 34. The computer-readable storagemedium of claim 33, wherein the subbands in each group are distributedacross T total subbands, and wherein the subbands in each group areinterlaced with the subbands in other groups in same symbol period. 35.The computer-readable storage medium of claim 31, wherein each datastream is independently processed with a coding and modulation schemeselected for the data stream to obtain the corresponding data symbolstream.
 36. The computer-readable storage medium of claim 31, whereineach of the plurality of data streams is independently encoded using abase inner code and an inner code rate selected for the data stream. 37.The computer-readable storage medium of claim 31, wherein transmissionunits are allocated to each data stream based on an information datarate of the data stream.
 38. The computer-readable storage medium ofclaim 31, wherein transmission units are allocated to the plurality ofdata streams in each frame of a predetermined time duration.
 39. Thecomputer-readable storage medium of claim 31, wherein the multi-carriercommunication system utilizes orthogonal frequency division multiplexing(OFDM).
 40. The computer-readable storage medium of claim 31, furthercomprising: instructions to select at least one data stream forrecovery; instructions to determine the transmission units used for eachselected data stream; instructions to obtain by the receiver detecteddata symbols for each selected data stream, each detected data symbolbeing an estimate of a corresponding data symbol broadcast by atransmitter; instructions to demodulate detected data symbols fromtransmission units used for each selected data stream onto a detecteddata symbol stream for the selected data stream, wherein at least onedetected data symbol stream is obtained for the at least one data streamselected for recovery; and instructions to process each of the at leastone detected data symbol stream to obtain a corresponding decoded datastream.
 41. A method of transmitting a plurality of data streams in awireless communication system, comprising: for each frame of apredetermined time duration, identifying a plurality of data processingunits for processing a plurality of data streams to be sent in theframe, processing at least one data block for each of the plurality ofdata streams to obtain at least one code block for the data stream, onecode block for each data block, each code block including a plurality ofdata symbols, allocating transmission units in the frame to each of theplurality of data streams, each transmission unit corresponding in onesymbol period and being usable to transmit one data symbol in a subband,mapping data symbols in at least once code block for each data stream torespective transmission units allocated to the corresponding datastream; and forming a composite symbol stream with overhead symbols anddata symbols, for the plurality of data streams, mapped to respectiveallocated transmission units of a current frame, wherein each of theplurality of data streams is independently recoverable by a receiverusing the overhead symbols included in the composite symbol stream, theoverhead symbols of the current frame indicating an allocation and anassignment of a corresponding data stream transmitted in another framethat is subsequent to the current frame.
 42. The method of claim 41,wherein the receiver determines which of the plurality of data streamsto independently recover based on the data symbols included in thecomposite symbol stream for the data stream.
 43. An apparatus in awireless communication system, comprising: means for identifying, foreach frame of a predetermined time duration, a plurality of dataprocessing units for processing a plurality of data streams to be sentin the frame, means for processing, for each frame of a predeterminedtime duration, at least one data block for each of the plurality of datastreams to obtain at least one code block for the data stream, one codeblock for each data block, each code block including a plurality of datasymbols, means for allocating, for each frame of a predetermined timeduration, transmission units in the frame to each of the plurality ofdata streams, each transmission unit corresponding in one symbol periodand being usable to transmit one data symbol in a subband, means formapping, for each frame of a predetermined time duration, data symbolsin at least once code block for each data stream to respectivetransmission units allocated to the corresponding data stream; and meansfor forming, for each frame of a predetermined time duration, acomposite symbol stream with overhead symbols and data symbols, for theplurality of data streams, mapped to respective allocated transmissionunits of a current frame, wherein each of the plurality of data streamsis independently recoverable by a receiver using the overhead symbolsincluded in the composite symbol stream, the overhead symbols of thecurrent frame indicating an allocation and an assignment of acorresponding data stream transmitted in another frame that issubsequent to the current frame.
 44. The apparatus of claim 43, whereinthe receiver determines which of the plurality of data streams toindependently recover based on the data symbols included in thecomposite symbol stream for the data stream.
 45. An apparatus in awireless communication system, comprising: a processing systemconfigured to: identify, for each frame of a predetermined timeduration, a plurality of data processing units for processing aplurality of data streams to be sent in the frame, process, for eachframe of a predetermined time duration, at least one data block for eachof the plurality of data streams to obtain at least one code block forthe data stream, one code block for each data block, each code blockincluding a plurality of data symbols, allocate, for each frame of apredetermined time duration, transmission units in the frame to each ofthe plurality of data streams, each transmission unit corresponding inone symbol period and being usable to transmit one data symbol in asubband, map, for each frame of a predetermined time duration, datasymbols in at least once code block for each data stream to respectivetransmission units allocated to the corresponding data stream; and form,for each frame of a predetermined time duration, a composite symbolstream with overhead symbols and data symbols, for the plurality of datastreams, mapped to respective allocated transmission units of a currentframe, wherein each of the plurality of data streams is independentlyrecoverable by a receiver using the overhead symbols included in thecomposite symbol stream, the overhead symbols of the current frameindicating an allocation and an assignment of a corresponding datastream transmitted in another frame that is subsequent to the currentframe.
 46. The apparatus of claim 45, wherein the receiver determineswhich of the plurality of data streams to independently recover based onthe data symbols included in the composite symbol stream for the datastream.
 47. A non-transitory computer-readable storage medium, in awireless communication system, storing instructions thereon, comprising:instructions to identify, for each frame of a predetermined timeduration, a plurality of data processing units for processing aplurality of data streams to be sent in the frame, instructions toprocess, for each frame of a predetermined time duration, at least onedata block for each of the plurality of data streams to obtain at leastone code block for the data stream, one code block for each data block,each code block including a plurality of data symbols, instructions toallocate, for each frame of a predetermined time duration, transmissionunits in the frame to each of the plurality of data streams, eachtransmission unit corresponding in one symbol period and being usable totransmit one data symbol in a subband, instructions to map, for eachframe of a predetermined time duration, data symbols in at least oncecode block for each data stream to respective transmission unitsallocated to the corresponding data stream; and instructions to form,for each frame of a predetermined time duration, a composite symbolstream with overhead symbols and data symbols, for the plurality of datastreams, mapped to respective allocated transmission units of a currentframe, wherein each of the plurality of data streams is independentlyrecoverable by a receiver using the overhead symbols included in thecomposite symbol stream, the overhead symbols of the current frameindicating an allocation and an assignment of a corresponding datastream transmitted in another frame that is subsequent to the currentframe.
 48. The non-transitory computer-readable storage medium of claim47, wherein the receiver determines which of the plurality of datastreams to independently recover based on the data symbols included inthe composite symbol stream for the data stream.